1. Field of the Invention
This invention relates to seal rings formed from generally rigid materials which are subject to deformation when employed in applications creating high differential pressures across the seal rings.
2. Description of the Prior Art
In a number of seal applications, the sealing function is accomplished by use of a seal ring formed from a material such as carbon or carbon-graphite which may be subjected to deformation when employed in an application where a high pressure difference is imparted across the seal ring. One such application is described in my U.S. Pat. No. 5,137,284, issued Aug. 11, 1992, which describes a stationary seal ring assembly for use in dry gas face seals. This patent is also assigned to Stein Seal Co. and is incorporated herein by reference. In the aforementioned patent, a stationary seal ring performs a sealing action with a movable runner mounted on a rotating shaft. The seal ring is provided with surfaces, some of which are exposed to high system pressure and others of which are exposed to lower system pressure. The seal ring may deform under these pressure loads where the differential pressure across the ring is very high. In the embodiment illustrated in my patent, such deformation is absorbed by the use of a metallic shroud or strong back which overlies one of the axial end surfaces and portions of the two radial surfaces of the seal ring. O-ring recesses are provided in the shroud and O-rings are inserted in each of the O-ring recesses to engage the adjacent surfaces of the shroud and the ring to prevent leakage. The one axial surface of the ring has a passageway extending therefrom entirely through the seal ring to a low pressure region of the seal housing to conduct any leakage through the O-rings to the low pressure region. The assembly of the O-rings, the shroud and the seal ring as described in my aforementioned patent can be improved for certain applications, e.g., for ease of assembly and to absorb small but important dimensional differences which occur in manufacture. In my patent, it is pointed out that the O-rings are pre-loaded for sealing in the axial sense only and are sized at their outer diameter to be larger than the inner diameter of the shroud to affect the seal at that location. In assembly of these components, difficulty can be encountered in that either (1) the O-rings do not seat at the sealing surfaces, or (2) the squeeze pre-load is very high due to tolerance stack-up, causing an out-of-flat condition to prevail at the sealing face. The out-of-flat condition is, of course, intolerable because effective sealing is not achieved. Furthermore, this out-of-flat condition is more serious on large diameter parts where high durometer O-rings are required to prevent extrusion and to combat explosive decompression at high operating pressure. In addition, it is to be noted that tolerance stack-up in the manufacture of the shroud, seal ring and O-rings can serve to reduce the effective seal between the O-rings and the shroud and seal ring or in other circumstances, to provide such increased forces on the seal ring as to create distortion thereof. This distortion or increased pressure on the seal ring caused by the O-rings is added to during seal operation with high pressure drops across the seal due to system operating parameters.